A Modified Fitzhugh-Nagumo Model that Reproduces the Action Potential and Dynamics of the Ten Tusscher et. al. Cardiac Model in Tissue

The two-variable Fitzhugh-Nagumo (FHN) model is a widely used cardiac and neural action potential simulating model due to its simplicity; however, it lacks many of the dynamics observed in cardiac experiments that can be reproduced by complex ionic cell models, such as the 19-variable Ten Tusscher et. al. (TNNP) model. We have parameterized a modified version of the FHN model that reproduces the dynamics in space of more complex cardiac cell models. We combined a series of modifications that previously were applied to the FHN model – mainly, the addition of a nullcline at zero voltage for the fast variable, that eliminates the hyperpolarization of the traditional FHN model and the modification of the slow nullcline from linear to quadratic, which allows for alternan behavior and a better fit to experiments and other models. This new model is fitted using particle swarm optimization (PSO) to fit the action potential for a large number of pacing periods so that the restitution of the action potential is matched between the two models. We created a modified FHN model that matches most of the AP shape of the TNNP model for a large range of periods and dynamics in space. This model allows for faster proof of concept investigations that can then help guide the more time-consuming simulations with complex ionic models.